Parallax Distance Calculator

Calculate the distance to a star based on its parallax angle measured in arcseconds.

Parallax Angle (arcseconds)

About Parallax Distance Calculation

The parallax method is one of the most fundamental techniques used by astronomers to measure the distances to nearby stars. As Earth orbits the Sun, relatively close stars appear to shift position against the background of more distant stars.

How It Works

This apparent shift, called stellar parallax, is measured in arcseconds (1/3600 of a degree). The smaller the parallax angle, the farther away the star is.

The Formula

Distance (parsecs) = 1 ÷ Parallax (arcseconds)

1 parsec ≈ 3.26 light-years
1 parsec ≈ 206,265 astronomical units (AU)
1 astronomical unit (AU) ≈ 149.6 million kilometers
1 light-year ≈ 9.46 trillion kilometers

Instructions

Enter the parallax angle in arcseconds (e.g., 0.125")
Click the calculate button
View the calculated distance in parsecs, light-years, and astronomical units

Frequently Asked Questions

What is a parallax angle?

A parallax angle is the apparent shift in position of a nearby star when observed from opposite sides of Earth's orbit around the Sun. This shift is measured in arcseconds (1/3600 of a degree).

Why is the parallax method limited to nearby stars?

As the distance increases, the parallax angle becomes extremely small and difficult to measure accurately. Most ground-based telescopes can only measure parallaxes down to about 0.01 arcseconds, which limits reliable measurements to stars within approximately 100 parsecs (about 326 light-years).

What does 'parsec' mean?

The term 'parsec' comes from 'parallax second', meaning a distance at which a star would show a parallax angle of exactly one arcsecond. One parsec equals approximately 3.26 light-years or 206,265 astronomical units.

What is an astronomical unit (AU)?

An astronomical unit is the average distance between the Earth and the Sun, approximately 149.6 million kilometers. It's commonly used to express distances within our solar system.

How accurate are parallax measurements today?

Modern space-based observatories like Gaia have achieved unprecedented accuracy, measuring parallaxes as small as 0.00001 arcseconds. This allows astronomers to determine distances to millions of stars with high precision across thousands of light-years.

Can this calculator be used for very large distances?

This calculator works best for relatively nearby stars where parallax angles are measurable. For objects beyond a few hundred parsecs, other methods such as standard candles (Cepheid variables, supernovae) or redshift measurements are required to determine distances.